1. Field of the Invention
This invention is directed to an inflator, or gas generator, used to rapidly provide a quantity of non-toxic gas suitable for inflating an inflatable article, such as the inflatable cushion of an airbag passive restraint system as used in modern vehicles. The invention is particularly directed to those inflators which rely on the ignition of solid pyrotechnic materials to create the required inflation gases.
2. Description of Related Art
Airbags which actuate in response to a collision to protect the occupants of a vehicle from more serious injury by providing a cushion between the occupants and the interior surfaces of the passenger compartment have become increasingly popular in modern vehicles due to their proven effectiveness. Airbag systems typically include one or more airbags mounted in a folded, deflated condition in a storage area in the passenger compartment. In the event of a collision, a crash sensor mounted on the vehicle's frame or body detects the sudden deceleration of the vehicle and electrically triggers activation of the airbag. Typical prior art airbag systems include a gas generator, or inflator, which contains a pyrotechnic gas generating material, or gas generant, which is capable, upon ignition, to rapidly form sufficient gas to inflate the associated airbag. The system also includes an initiator, such as an electric squib, and an igniter or a similar ignition enhancing charge of a rapidly igniting material, such as boron potassium nitrate (BKNO.sub.3). Upon receipt of a triggering signal from the crash sensor, the initiator fires causing the rapid combustion of the rapidly igniting material, which, in turn, ignites the slower burning gas generant.
Airbag systems used on the passenger side of vehicles are usually mounted at a location behind the instrument panel/dashboard. As described in U.S. Pat. Nos. 4,005,876, to Jorgenson et al., issued Feb. 1, 1977, and 4,878,690, to Cunningham, issued Nov. 7, 1989, such systems usually include a gas generator having a cylindrical housing. An electric initiator, or squib, is located at one end of the housing so as to fire upon a linear igniter comprising an igniter tube extending along the axis of the housing. The igniter tube is loaded with igniter granules, and often includes a fuse of rapid deflagration cord (RDC) extending along the tube's axis and surrounded by igniter granules whereby it assures even ignition along the length of the inflator. One end of the igniter tube is closed with a screen which retains the igniter granules while permitting ignition of the granules by an auto-ignition device in the event of a vehicle fire. An exposed length of the RDC and a stand of f distance between the igniter and the auto-ignition device are critical features which must be closely monitored during assembly of the inflator to assure proper operation of the auto ignition device. The gas generant material, in pellet or wafer form, surrounds the igniter tube along the length of the housing. The gas generant material, in turn, is surrounded by a filtering and cooling structure which cools the generated gas and filters particulates therefrom prior to the gas discharging through openings in the cylindrical wall of the housing to the interior of the airbag, thereby inflating same. Many variations of the prior art inflators and their linear igniters are presently in use and work well. Such variations include those described in U.S. Pat. Nos. 5,620,205 and 5,626,360. These igniters, however, require labor intensive assembly and are generally comprised of many components, some of which are costly.
Igniters have also been designed to be mounted at one end of elongated cylindrical gas generators. Such an igniter, which uses a particulate or granular ignition material, is described in commonly assigned U.S. Pat. No. 5,409,259, granted Apr. 25, 1995 to Cunningham et al.; and in a continuation-in-part application of that patent, Ser. No. 08/106,291, entitled "Gas Generator For Vehicle Occupant Restraint System", filed on Aug. 13, 1993. An end mounted pyrogen igniter which includes a solid grain of a pyrotechnic gas generant material is disclosed in U.S. Pat. No. 5,623,115.
The igniters of the prior art are relatively expensive to make and install. Additionally, they contain non-consumable materials which can produce hot particulate residue that must be removed from the generated gas to prevent its damaging the airbag during the inflation thereof. Vehicle vibrations can cause some igniters to break. Moreover, some igniters have caused the associated solid gas generant to break or disintegrate during ignition, resulting in the inflator exhibiting non-uniform and poorly controlled burn and inflation gas delivery characteristics. Finally, the delay time occurring between receipt of the activation signal and pressurization of the airbag during which the various materials in the ignition train sequentially ignite can be longer than is optimum. A need continues to exist for less complicated, more easily assembled and less costly ignition systems which provide rapid and uniform ignition, while maintaining a high degree of safety and reliability.